Installation for the purification of minerals, pigments and/or fillers and/or the preparation of precipitated earth alkali carbonate

ABSTRACT

The present invention relates to an installation for the purification of minerals, pigments and/or fillers and/or the preparation of precipitated earth alkali carbonate and/or mineralization of water and to the use of such an installation for the purification of minerals, pigments and/or fillers and/or mineralization of water and/or the preparation of precipitated earth alkali carbonate.

The present invention relates to an installation for the purification ofminerals, pigments and/or fillers and/or the preparation of precipitatedearth alkali carbonate and/or mineralization of water and to the use ofsuch an installation for the purification of minerals, pigments and/orfillers and/or mineralization of water and/or the preparation ofprecipitated earth alkali carbonate.

Pure minerals, pigments and/or fillers are used extensively in paper,paper coatings, plastics and paints but also in the food and feedindustry, water mineralization and pharmaceutical industry. For example,calcium carbonate, a low cost and high brightness filler, is widely usedto increase sheet brightness and opacity in paper products. Its use hasincreased dramatically in the last decades due to the conversion fromacid to alkaline papermaking at paper mills. Both natural and syntheticcalcium carbonates are used in the paper industry. For instance, naturalcalcium carbonate, such as marble, chalk and limestone, is ground to asmall particle size prior to its use in paper products, while syntheticcalcium carbonate is manufactured by a precipitation reaction and istherefore called precipitated calcium carbonate.

Besides its use in the papermaking industry, natural and syntheticcalcium carbonate are also used for various other purposes, e.g. asfiller or pigment in paint industries, and as functional filler for themanufacture of plastic materials, plastisols, sealing compounds,printing inks, rubber, toothpaste, cosmetics, food, pharmaceuticals etc.In addition thereto, calcium carbonate can also be used for thetreatment and mineralization of water.

Due to the foregoing comments, the industry has a strong demand forefficient and economic devices and systems to prepare pure minerals,pigments and/or fillers. The term “pure” minerals, pigments and/orfillers especially refers to the corresponding mineral, pigment and/orfiller phase being free of chemical additives or unwanted impuritieswhich are limiting the use in many applications due to the lowbrightness of colored impurities. Such impurities are derived fromsilicates and/or process additives such as fatty amines or quaternaryammonium compound used in flotation.

In this regard, the applicant is aware of several installations for thepurification of minerals, pigments and/or fillers. For example,reference is made to installations used for froth flotation processese.g. as described in the book “FROTH FLOTATION”, A Century of Innovationby Maurice C. Fuerstenau, published by Society for Mining, Littleton,Colo., USA, 2007, on pages 635 to 757.

However, the described installations and processes have the disadvantagethat specific additives such as collectors, frothers or depressants arerequired which again contaminate the obtained mineral, pigment and/orfiller phase. Such impurities typically prohibit the use of suchobtained mineral, pigment and/or filler phase for example as nutrientsin food and feed or, alternatively, require an additional cost and timeconsuming cleaning step.

It should be further noted that the efficiency of said installations andprocesses rapidly decreases with increasing fineness of the respectiveimpurity particles in the mineral, pigment and/or filler phase such thatthe extraction of a specific part of minerals out of a blend ofminerals, e.g. calcium carbonate out of a blend of impure marble, ismore complicated. In particular, the selectivity of said installationsand processes decreases because the separation of different mineralphases from each other strongly depends on the degree of particleintergrowths in the mineral, pigment and/or filler phase.

The term “degree of particle intergrowth” (particle size of liberation)in the meaning of the present application refers to the size ofparticles where the different mineral, pigment and/or filler phases areseparated from each other.

Also physical separation devices are known in the art. However, e.g.optical sorting has also the disadvantage of limited selectivity due tothe degree of particle intergrowths and, furthermore, that sufficientcolour contrasts of the particles to be separated is required. Otherphysical separation devices include X-ray sorting, electrical sorting,screening and/or filtration facing the same problems.

In this regard, one typical prior art installation is shown in theschematic diagram according to FIG. 1. The exemplified installationcomprises a mixing unit (1) such as a tank equipped with a stirrer, oneinlet for the introduction of water (14), one gas inlet (not shown),e.g. a CO₂ inlet, and a further inlet for the introduction of minerals,pigments and/or fillers to be purified (6) which are preferably providedin form of a suspension. The mixing unit further comprises one inlet andone outlet independently connected to a filtration unit (4).Accordingly, also the filtration unit (4) comprises one inlet and oneoutlet independently connected to the mixing unit (1). In other words,the filtration unit (4) and the mixing unit (1) are provided in acircular arrangement, i.e. both units are in a fluid communication witheach other. Furthermore, the filtration unit (4) is equipped with anadditional outlet (not shown) for discharging of the filtrate (10)obtained by the filtration process. The discharged filtrate (10) may besubjected to further treatments (16) such as physical and/or chemicaltreatments and/or the addition of additives. In contrast, the filtrandor retentate obtained in the membrane filtration unit (4) is circulatedback into the mixing unit (1).

Herein, the minerals, pigments and/or fillers to be purified could,however, not or only very ineffectively be cleaned up to now. Inparticular, particle intergrowths in the mineral, pigment and/or fillerphase limit the selectivity and, thus, the purification efficiency ofthe described installation. Therefore, for the purification of minerals,pigments and/or fillers only particulate materials having a particularfineness could be used as starting materials which, however, areavailable only to a limited extend.

Again, the foregoing physical separation devices have the limitationthat their efficiency strongly depends on the degree of particleintergrowth in the mineral, pigment and/or filler phase. Thus, theselectivity of said devices also decreases with an increasing degree ofintergrowth of particles.

Furthermore, the expert also faces disadvantages if the particleintergrown in the mineral, pigment and/or filler phase are divided atonce and/or below their degree of particle intergrowth as the resultingparticles in the mineral, pigment and/or filler phase are ultrafine. Inparticular, a sudden particle separation may lead to selectivityproblems in e.g. a flotation process because the mineral slime mayfeature a decreased settling behavior. As a consequence, this may leadto uncontrolled overflow of the fines with the froth concentrate. Inthis regard, a mineral recovery of only 50 wt.-% or even less isfrequently observed. The foregoing is well known in the industry todayand has to be overcome by a process step called “de-sliming” of thecorresponding suspension. De-sliming of a suspension means that theultrafine part of particles in the suspension is mechanically extracted,separated from the whole and discharged. Up to half of the valuableminerals, which are cost and time consuming to extract, end up in thetailing piles. As a result, the recovered concentrate causes highproduction costs.

For better understanding of the problem of intergrowths in mineral,pigment and/or filler phases, reference is made to Ullmann'sEncyclopedia of Industrial Chemistry, Potassium Compounds, Part 4.1.Inter-growth and Degree of Liberation, June 2002, Wiley-VCH Verlag GmbH& Co. KgaA.

Thus, the main disadvantage of the existing devices and installationstoday is the fact that the selectivity is still very limited. Inparticular, the degree of particle intergrowths in the mineral, pigmentand/or filler phase represents a decisive limiting factor. In additionthereto, the reactivity of solid particles strongly depends on theparticle surface chemistry. For instance, the particle surface may bemodified if it is exposed to the atmosphere (e.g. air), water or otherenvironmental influences, such as e.g. electro smog, and thus influencesthe reaction speed, adsorption and/or surface properties of theminerals, pigments and/or fillers. This aspect is especially relevantif, for example, dolomitic minerals are to be used to remineralizedesalinated sea water as the reactivity between dolomite and CO₂ israther slow. Corresponding industrial processes known in the art are notable to overcome the problems associated with such modified particlesurface.

In addition thereto, the applicant is also aware of devices andinstallations for the preparation of precipitated earth alkali carbonatesuch as precipitated calcium carbonate (PCC) which may be obtained bythe precipitation of calcium oxide/calcium hydroxide in an aqueousenvironment by using gaseous CO₂. The prior art installation shown inthe schematic diagram according to FIG. 1 may be also used for thepreparation of precipitated earth alkali carbonate such as precipitatedcalcium carbonate (PCC). However, said precipitation reactions in suchinstallations are often non-satisfying because encapsulated CaO andCa(OH)₂ or the respective species may be found in the aggregates ofproduced PCC or precipitated earth alkali carbonate. In particular, thegaseous/solid/liquid interphases obtained during the precipitationprocess at solids content of e.g. 15 wt.-% and above are difficult tocontrol. In this context, it should be further noted that afterprecipitation and formation of precipitated earth alkali carbonate likePCC in an aqueous environment such encapsulated alkaline residualspecies may migrate during storage out of the precipitated earth alkalicarbonate aggregates into the aqueous phase which may lead to a pHincrease of the suspension in an uncontrolled way even to above a pH of12. Such pH increase, however, may damage the precipitated earth alkalicarbonate suspension performance and may influence later applications,such as in paper coatings and fillings. The precipitation devices andinstallations known in the art are not able to solve these problems.

In the art, several approaches for solving the foregoing problems areproposed. For instance, EP1764346 A1 describes a device and process forgrinding of PCC after precipitation. During this process residual,encapsulated CaO and Ca(OH)₂ in the aggregates are released and increasethe pH of the resulting suspension. This may not only result again in areduced performance of the PCC suspension in later applications, such aspaper coatings and fillings, but may also damage and dissolve thegrinding beads used during the process.

In view of the foregoing, improving the purification of minerals,pigments and/or fillers and/or the preparation of precipitated earthalkali carbonate still remains of interest to the skilled man. It wouldbe especially desirable to provide an alternative and improved systemfor the purification of minerals, pigments and/or fillers and/or thepreparation of precipitated earth alkali carbonate and/or mineralizationof water which can be applied in a more efficient, economic and ecologicway and especially provides a sufficient selectivity and/or reactivityfor the preparation of pure minerals, pigments and/or fillers and/orprecipitated earth alkali carbonate.

The foregoing and other objects are solved by the provision of aninstallation for the purification of minerals, pigments and/or fillersand/or the preparation of precipitated earth alkali carbonate and/ormineralization of water, the installation comprising in fluidcommunication

-   -   a) at least one mixing unit provided with at least two inlets        and at least one outlet,    -   b) at least one dividing unit comprising dividing means, and    -   c) at least one membrane filtration unit provided with at least        one inlet and at least one outlet,        wherein at least one outlet of the at least one mixing unit is        connected to at least one inlet of the at least one membrane        filtration unit and at least one outlet of the at least one        membrane filtration unit is connected to at least one inlet of        the at least one mixing unit.

As used herein, the term “in fluid communication” means that the unitsand/or devices being part of the inventive installation are coupled witheach other such that a flow of fluid such as of a suspension optionallyin combination with at least one inverse aerosol (such as a very finefoam) from one unit and/or device of the inventive installation toanother unit and/or device of the inventive installation is possible;such flow may be achieved by way of one or more intermediate (and notspecifically mentioned or described) components, apparatuses, devices orother articles like tubes, pipes and pumps. The term “inverse aerosol”is to be interpreted broadly and means any gas suspended in a liquid,for example very small CO₂ gas bubbles in water.

The term “purification” is to be interpreted broadly and means anyremoval of compounds not tolerated or wanted in the mineral, pigmentand/or filler phase.

The term “mineralization” as used in the present invention refers to theincrease of essential mineral ions in water not containing mineral ionsat all or in insufficient amount to obtain water that is palatable. Amineralization can be achieved by adding at least calcium carbonate tothe water to be treated. Optionally, e.g., for health-related benefitsor to ensure the appropriate intake of some other essential mineral ionsand trace elements, further substances may be mixed with the calciumcarbonate and then added to the water during the remineralizationprocess. According to the national guidelines on human health anddrinking water quality, the remineralized product may compriseadditional minerals containing magnesium, potassium or sodium, e.g.,magnesium carbonate, magnesium sulfate, potassium hydrogen carbonate,sodium hydrogen carbonate or other minerals containing essential traceelements.

“Ground calcium carbonate (GCC)” in the meaning of the present inventionis a calcium carbonate obtained from natural sources including marble,chalk or limestone, and processed through a treatment such as grinding,screening and/or fractionizing wet and/or dry, for example, by acyclone.

“Precipitated earth alkali carbonate” in the meaning of the presentinvention is a synthesized material, generally obtained by precipitationfollowing the reaction of carbon dioxide and e.g. lime in an aqueousenvironment or by precipitation of an earth alkali and carbonate sourcein water or by precipitation of earth alkali and carbonate ions, forexample CaCl₂ and Na₂CO₃, out of suspension. For example, precipitatedcalcium carbonate exists in three primary crystalline forms: calcite,aragonite and vaterite, and there are many different polymorphs (crystalhabits) for each of these crystalline forms. Calcite has a trigonalstructure with typical crystal habits such as scalenohedral (S-PCC),rhombohedral (R-PCC), hexagonal prismatic, pinacoidal, colloidal(C-PCC), cubic, and prismatic (P-PCC). Aragonite is an orthorhombicstructure with typical crystal habits of twinned hexagonal prismaticcrystals, as well as a diverse assortment of thin elongated prismatic,curved bladed, steep pyramidal, chisel shaped crystals, branching tree,and coral or worm-like forms.

The inventors of the present invention surprisingly found out that suchan installation enables the skilled person to prepare minerals, pigmentsand/or fillers and/or precipitated earth alkali carbonate with highpurity in an efficient, economic and ecologic way. The inventors of thepresent invention further surprisingly found out that such aninstallation enables the skilled person to mineralize water with highefficiency in an economic and ecologic way. In particular, this isachieved by providing at least one mixing unit, at least one dividingunit, and at least one membrane filtration unit which are connected influid communication. Furthermore, at least one inlet and at least oneoutlet of the membrane filtration unit are independently connected tothe at least one mixing unit.

Thus, the instant installation enables an increase of the overallselectivity of a purification process to be achieved for minerals,pigments and/or fillers installation for the purification of minerals,pigments and/or fillers and/or the preparation of precipitated earthalkali carbonate.

According to another aspect of the present invention, the use of saidinstallation for the purification of minerals, pigments and/or fillersand/or mineralization of water is provided. According to a furtheraspect of the present invention, the use of said installation for thepreparation of precipitated earth alkali carbonate is provided.

Advantageous embodiments of the present invention are defined in thecorresponding sub-claims.

When in the following reference is made to preferred embodiments ortechnical details of the inventive installation, it is to be understoodthat these preferred embodiments or technical details also refer to theinventive uses of the installation for the purification of minerals,pigments and/or fillers and/or mineralization of water and/or thepreparation of precipitated earth alkali carbonate as defined herein andvice versa (as far as applicable). If, for example, it is set out thatthe at least one mixing unit of the inventive installation comprises astirring device also the at least one mixing unit of the inventive usescomprises a stirring device.

The present invention will be described with respect to particularembodiments and with reference to certain figures but the invention isnot limited thereto but only by the claims. Terms as set forthhereinafter are generally to be understood in their common sense unlessindicated otherwise.

Where the term “comprising” is used in the present description andclaims, it does not exclude other non-specified elements of major orminor functional importance. For the purposes of the present invention,the term “consisting of” is considered to be a preferred embodiment ofthe term “comprising of”. If hereinafter a group is defined to compriseat least a certain number of embodiments, this is also to be understoodto disclose a group, which preferably consists only of theseembodiments.

Whenever the terms “including” or “having” are used, these terms aremeant to be equivalent to “comprising” as defined above.

Where an indefinite or definite article is used when referring to asingular noun, e.g. “a”, “an” or “the”, this includes a plural of thatnoun unless something else is specifically stated.

According to one embodiment of the present invention, the at least onemixing unit comprises a stirring device.

According to another embodiment of the present invention, the at leastone mixing unit comprises a heating device capable of heating thecontent of the at least one mixing unit to a temperature of between 5°C. and 90° C., and preferably between 20° C. and 50° C.

According to yet another embodiment of the present invention, the atleast one dividing unit is at least one grinding device and/or at leastone crushing device, and preferably is at least one grinding device.

According to one embodiment of the present invention, the at least onedividing unit is at least one vertical grinding device and/or at leastone vertical crushing device or at least one horizontal grinding deviceand/or at least one horizontal crushing device.

According to another embodiment of the present invention, the at leastone dividing unit is a conical annular gap bead mill.

According to yet another embodiment of the present invention, the atleast one dividing unit comprises dividing means having a weight medianparticle diameter d₅₀ value of from 0.01 mm to 100 mm, preferably from0.1 mm to 75 mm and most preferably from 0.5 mm to 5 mm.

According to one embodiment of the present invention, the at least onedividing unit comprises moving beads as dividing means made of amaterial selected from the group comprising quartz sand, glass,porcelain, zirconium oxide, zirconium silicate and mixtures thereof,optionally comprising minor quantities of further minerals.

According to another embodiment of the present invention, the dividingmeans of the at least one dividing unit are made of a mineral, pigmentand/or filler material, preferably the dividing means and the minerals,pigments and/or fillers to be purified and/or to be prepared are of thesame material.

According to yet another embodiment of the present invention, the atleast one membrane filtration unit is a cross flow membrane filtrationdevice, and preferably is a cross flow membrane micro filtration deviceand/or a cross flow membrane ultrafiltration device. It is preferredthat the cross flow membrane filtration device comprises at least onetube filter membrane having an inner diameter of the tube from 0.01 mmto 25 mm, preferably from 0.1 mm to 10 mm.

According to one embodiment of the present invention, the at least onemembrane filtration unit comprises at least one membrane having a poresize of between 0.01 μm and 10 μm, preferably between 0.05 and 5 μm andmost preferably between 0.1 and 2 μm. It is preferred that the membranematerial is selected from the group comprising a sintered material,porous porcelain, synthetic polymers, like polyethylene, polypropyleneor Teflon®, and mixtures thereof.

According to another embodiment of the present invention, the speed offlow across the at least one membrane of the cross flow membranefiltration device is between 0.1 m/s and 10 m/s, preferably between 0.5m/s and 5 m/s and most preferably between 1 m/s and 4 m/s and/or thepressure at the inlet of the cross flow membrane filtration device isbetween 0 bar and 30 bar, preferably between 0.2 bar and 10 bar and mostpreferably between 0.5 and 5 bar.

According to yet another embodiment of the present invention, theinstallation comprises at least three outlets, preferably at least fouroutlets and more preferably at least five outlets and/or theinstallation comprises at least four inlets, preferably at least fiveinlets and more preferably at least six inlets.

According to one embodiment of the present invention, the at least onemixing unit comprises at least two outlets and/or at least three inlets,preferably at least four inlets.

According to another embodiment of the present invention, at least oneinlet provided with the installation is a gas inlet, preferably a CO₂inlet.

According to one embodiment of the present invention, the at least onemixing unit comprises at least two inlets being liquid inlets,preferably at least three liquid inlets, and more preferably at leastfour liquid inlets.

According to another embodiment of the present invention, theinstallation comprises at least one control unit regulating the fillinglevel of the at least one mixing unit, pump speed, pH, conductivity,calcium ion concentration (e.g. by ion sensitive electrode) and/ortemperature.

According to yet another embodiment of the present invention, theinstallation comprises at least one pump located between the at leastone mixing unit and the at least one membrane filtration unit.

According to one embodiment of the present invention, at least oneoutlet of the at least one mixing unit is connected to at least oneinlet of the at least one dividing unit and at least one outlet of theat least one dividing unit is connected to at least one inlet of the atleast one mixing unit.

According to another embodiment of the present invention, theinstallation further comprises at least one pump located between the atleast one mixing unit and the at least one dividing unit.

According to yet another embodiment of the present invention, thepumping capacity of the at least one pump (in m³/h of the sum) feedingthe at least one membrane filtration unit is 0.01 to 100 times thevolume of the at least one mixing unit and/or the ratio of the pumpingcapacity of the at least one pump (in m³/h of the sum) feeding the atleast one dividing unit to the pumping capacity of the at least one pump(in m³/h of the sum) feeding the at least membrane filtration unit isbetween 1:1 and 1:1000 and preferably between 1:5 and 1:250.

According to one embodiment of the present invention, the at least onedividing unit is integrated in the at least one mixing unit.

According to another embodiment of the present invention, at least oneinlet being a gas inlet is located between the at least one mixing unitand the at least one dividing unit, more preferably between a feed pumpof the at least one dividing unit and the at least one dividing unit,and most preferably at the inlet of the dividing unit.

According to yet another embodiment of the present invention, the atleast one inlet being a gas inlet is a venturi injector that is locatedbetween the at least one mixing unit and the at least one dividing unit.Preferably, the venturi injector is located between the outlet of the atleast one mixing unit and the inlet of the at least one dividing unit.

According to one embodiment of the present invention, at least one inletbeing a gas inlet is located at the top of the hollow shaft of thestirring device of the at least one mixing unit.

The present invention is now described in more detail:

Thus, the present invention provides an installation for thepurification of minerals, pigments and/or fillers and/or mineralizationof water and/or the preparation of precipitated calcium carbonate, theinstallation comprising in fluid communication

-   -   a) at least one mixing unit provided with at least two inlets        and at least one outlet,    -   b) at least one dividing unit comprising dividing means, and    -   c) at least one membrane filtration unit provided with at least        one inlet and at least one outlet,        wherein at least one outlet of the at least one mixing unit is        connected to at least one inlet of the at least one membrane        filtration unit and at least one outlet of the at least one        membrane filtration unit is connected to at least one inlet of        the at least one mixing unit.

The installation of the present invention is applicable to anypurification process carried out in a reactor system utilizing minerals,pigments and/or fillers irrespective of the degree of particleintergrowths and/or to the mineralization of water and/or to thepreparation of precipitated earth alkali carbonate.

For example, nearly pure precipitated earth alkali carbonate may beprepared in the inventive installation out of an impure material.

The precipitated earth alkali carbonate that may be prepared ispreferably selected from among, crystalline calcium carbonate in thecalcitic, the aragonitic or the vateritic form, magnesite andhydromagnesite, or is a mixture of the aforementioned.

The purification and preparation of precipitated earth alkali carbonatemay preferably be carried out in that water, at least one substancecomprising e.g. at least one earth alkali carbonate and optionally atleast one earth alkali hydroxide, wherein the at least one substance ispreferably provided in dry form or in aqueous suspended form, and CO₂are combined.

The at least one substance comprising at least one earth alkalicarbonate and optionally at least one earth alkali hydroxide ispreferably selected from natural calcium and/or magnesium carbonatecontaining inorganic substances or salts, or synthetic calcium and/ormagnesium carbonate containing inorganic substances or salts.

For example, the at least one substance comprising at least one earthalkali carbonate and optionally at least one earth alkali hydroxide ispreferably selected from the group comprising marble, limestone, chalk,half burnt lime, burnt lime, dolomitic limestone, calcareous dolomite,half burnt dolomite, burnt dolomite, and precipitated earth alkalicarbonates such as precipitated earth alkali carbonate, for example ofcalcitic, aragonitic and/or vateritic mineral crystal structure, forexample from water de-hardening by the addition of Ca(OH)₂.

Useful natural occurring inorganic substances are for example marble,limestone, chalk, dolomitic marble and/or dolomite. Synthetic substancesare for example precipitated calcium carbonates in the calcitic,aragonitic and/or vateritic crystalline form. However, natural occurringinorganic substances such as, for example, marble, limestone, chalk,dolomitic marble and/or dolomite are preferred.

The optional at least one earth alkali hydroxide is preferably calciumhydroxide and/or magnesium hydroxide. Due to the fact of very lowsolubility of Mg(OH)₂ in water compared to Ca(OH)₂ the speed of reactionof Mg(OH)₂ with CO₂ is very limited and in presence of Ca(OH)₂ insuspension the reaction of CO₂ with Ca(OH)₂ is very much preferred.Surprisingly, by using the inventive installation it is possible toproduce Mg(HCO₃)₂ rich earth alkali hydrogen carbonate suspension alsoin presence of Ca(OH)₂ in the suspension.

The at least one substance comprising at least one earth alkalicarbonate and the optional at least one earth alkali hydroxidepreferably has a weight median particle size (d₅₀) in the range of 0.1μm to 1 mm, and preferably in the range of 0.2 μm to 100 μm, morepreferably in the range of 0.5 to 25 μm, for example 0.7 to 3 μm.

Additionally or alternatively, the at least one substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide has preferably a specific surface area (SSA) in therange of 0.01 to 200 m²/g, and more preferably in the range of 1 to 100m²/g, for example 1 to 15 m²/g. For determining the specific surfacearea, a Mastersizer 2000 device from the company Malvern InstrumentsGmbH, Germany, was used.

The term “specific surface area (SSA)” in the meaning of the presentinvention describes the material property of pigments/minerals/solidsthat measures the surface area per gram of pigments. The unit is m²/g.

The term “total particle surface area (SSA_(total))” in the meaning ofthe present invention describes the total surface area per tonne ofsuspension S.

Throughout the present application, the “particle size” of a mineral,pigment and/or filler product is described by its distribution ofparticle sizes. The value d_(x) represents the diameter relative towhich x % by weight of the particles have diameters less than d_(x).This means that the d₂₀ value is the particle size at which 20 wt.-% ofall particles are smaller, and the d₇₅ value is the particle size atwhich 75 wt.-% of all particles are smaller. The d₅₀ value is thus theweight median particle size, i.e. 50 wt.-% of all grains are bigger orsmaller than this particle size. For the purpose of the presentinvention, the particle size is specified as weight median particle sized₅₀ unless indicated otherwise. These values were measured using aMastersizer 2000 device from the company Malvern Instruments GmbH,Germany.

Furthermore, the at least one substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxidemay have a hydrochloric acid (HCl) insoluble content from 0.02 to 90wt.-%, preferably from 0.05 to 15 wt.-%, based on the total weight ofthe dry substance. The HCl insoluble content may be, e.g., minerals suchas quartz, silicate, mica and/or pyrite.

The water is preferably selected from distilled water, tap water,desalinated water, brine, brackish water, treated wastewater or naturalwater such as ground water, surface water, sea water or rain water. Thewater may contain NaCl in an amount between 0 and 200 mg per liter.

Sea water or brackish water may be firstly pumped out of the sea by openocean intakes or subsurface intakes such as wells, and then it undergoesphysical pretreatments such as screening, sedimentation or sand removalprocess. Additional treatment steps such as coagulation and flocculationmay be necessary in order to reduce potential fouling on membranes usedin the inventive installation. The pretreated sea water or brackishwater may be further distilled, e.g., by using multiple stage flash,multiple effect distillation, or membrane filtration such asultrafiltration or reverse osmosis, to remove remaining particulates anddissolved substances.

The CO₂ is preferably selected from gaseous carbon dioxide, liquidcarbon dioxide, solid carbon dioxide or a gaseous mixture of carbondioxide and at least one other gas, and is preferably gaseous carbondioxide. When the CO₂ is a gaseous mixture of carbon dioxide and atleast one other gas, then the gaseous mixture is a carbon dioxidecontaining flue gas exhausted from industrial processes like combustionprocesses or calcination processed or alike. CO₂ can also be produced byreacting an alkali- and/or earth alkali carbonate with acid. The acidused in the present invention is preferably an inorganic acid such assulphuric acid, hydrochloric acid, phosphoric acid, and is preferablysulphuric acid or phosphoric acid. Preferably the alkali- and/or earthalkali carbonate to produce the CO₂ is a calcium carbonate comprisingearth alkali carbonate, more preferably the alkali- and/or earth alkalicarbonate is of the same quality as the at least one earth alkalicarbonate. If the CO₂ is produced by reacting an alkali- and/or earthalkali carbonate with acid, then the acid is preferably dosed directlyin the mixing unit (in the case where the dividing unit is integrated inthe mixing unit) or in the system after the outlet of the mixing unitand before the inlet of the dividing unit (e.g. for a system shown inFIG. 2) Furthermore, it can be produced by the combustion of organics,such as ethyl alcohol, wood and the like, or by fermentation. When agaseous mixture of carbon dioxide and at least one other gas is used,then the carbon dioxide is present in the range of 8 to about 99 vol.-%,and preferably in the range of 10 to 98 vol.-%, for example 95 vol.-%.CO₂ gas can also contain >99 vol.-%, for example ≧99.9 vol.-%.

Additionally or alternatively, the CO₂ preferably has a ¹⁴C decay of atleast 500, more preferably at least 800 and most preferably at least 850to 890 decays per h and per g of C in the CO₂.

In one preferred embodiment of the present invention, the amount of CO₂used, in mol, to produce 1 mol of at least one earth alkali hydrogencarbonate in the aqueous suspension out of calcium carbonate containingmaterial is in the range of only 0.5 to 4 mol, preferably in the rangeof only 0.5 to 2.5 mol, more preferably in the range of only 0.5 to 1.0mol, and most preferably in the range of only 0.5 to 0.65 mol.

In particular, the water, the at least one substance comprising at leastone earth alkali carbonate and the optional at least one earth alkalihydroxide and the CO₂ may be combined in order to obtain a suspension Shaving a pH of between 6 and 9, wherein the resulting suspension Scontains particles. Alternatively, the water and the at least onesubstance comprising at least one earth carbonate and the optional atleast one earth alkali hydroxide are combined in order to obtain analkaline aqueous suspension of at least one substance comprising atleast one earth alkali carbonate and the optional at least one earthalkali hydroxide, and subsequently the alkaline aqueous suspension iscombined with the CO₂ in order to obtain a suspension S having a pH ofbetween 6 and 9, wherein the suspension S contains particles.

In one preferred embodiment of the present invention, the aqueoussuspension of the at least one substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxide ina minor amount in respect to earth alkali carbonate, is freshly preparedby mixing the water and the substance comprising at least one earthalkali carbonate and the optional at least one earth alkali hydroxide ina minor amount in respect to earth alkali carbonate.

The term aqueous “suspension” in the meaning of the present inventioncomprises essentially insoluble solids and water and optionally furtheradditives and usually contains large amounts of solids and, thus, ismore viscous and generally of higher density than the liquid from whichit is formed. However, the term “essentially insoluble” does not excludethat at least a part of the solids material dissolves in water undercertain conditions, e.g. for water treatment.

The on-site preparation of the aqueous suspension may be preferred sincepremixing the aqueous suspensions may require the addition of furtheragents such as stabilizers or disinfectants. If disinfection is needed,preferably an inlet for hydrogen peroxide dosage is needed. If thesuspension contains residual NaCl disinfection can be achievedpreferably by installing a direct voltage (DC) electrolysis equipmentforming traces of Cl₂ as disinfectant. In addition, the direct voltage(DC) electrolysis equipment can be connected to and controlled by a Cl₂detector.

Combining and mixing the water and the substance comprising at least oneearth alkali carbonate and the optional at least one earth alkalihydroxide such that an aqueous suspension of the at least one substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide is preferably carried out in the at least onemixing unit provided with at least two inlets and at least one outlet asrequired for the inventive installation.

In this regard, it is appreciated that the at least one mixing unit maybe any kind of tank and/or vessel well known to the man skilled in theart for combining and/or mixing and/or stirring suspensions comprisingminerals, pigments and/or fillers.

For example, the at least one mixing unit may be a tank and/or vesselranging from 10 l to 100,000 kl, preferably from 50 l to 50,000 kl andmore preferably from 1,000 l to 25,000 kl.

Additionally or alternatively, the installation of the present inventioncomprises one mixing unit.

In one preferred embodiment of the present invention, the at least onemixing unit comprises a stirring device. For example, the stirringdevice is selected from mechanical stirring devices such as a stirringblade typically used for agitating and mixing suspensions comprisingminerals, pigments and/or fillers in a tank and/or vessel.Alternatively, the stirring device is selected from powder-liquid mixingdevices typically used for agitating and mixing more concentratedsuspensions comprising minerals, pigments and/or fillers in a tankand/or vessel.

In one preferred embodiment of the present invention, the stirringdevice is a mixing machine, wherein the mixing machine enablessimultaneous mixing of the aqueous suspension and dosing of gas, e.g.CO₂.

In another preferred embodiment of the present invention, the at leaston mixing unit may be equipped with a gas inlet which may be locatedsuch that the introduction of gas, e.g. CO₂, into the at least onemixing unit results in a sufficient agitation of the aqueous suspension.In one preferred embodiment of the present invention, at least one inletbeing a gas inlet is located at the top of the hollow shaft of thestirring device of the at least one mixing unit. When the gas inlet islocated at the top of the hollow shaft of the stirring device, the gas,e.g. CO₂, is introduced into the mixing unit by the vacuum that iscaused by the rotation of the stirring blades. However, the gas, e.g.CO₂, can also be introduced into the mixing unit through the top of thehollow shaft of the stirring device by applying at least some pressure.It is noted that the preferred embodiment for the introduction of thegas is one where the gas is introduced into the mixing unit by thevacuum that is caused by the rotation of the stirring blades.Furthermore, the at least one mixing unit may comprise agitation meanssuch as agitation beads.

Depending on the concentration of the resulting aqueous suspension S,the mixing time may be from 5 to 600 min, from 10 to 200 min, from 20 to100 min, or from 30 to 50 min.

The resulting aqueous suspension S has preferably a pH in the range of6.5 to 9, preferably in the range of 6.7 to 7.9, and most preferably inthe range of 6.9 to 7.7, at 20° C.

According to one embodiment of the present invention, the aqueous phaseof the resulting aqueous “suspension S” has a calcium ion concentrationfrom 1 to 700 mg/l, preferably from 50 to 650 mg/l, and most preferablyfrom 70 to 630 mg/l. According to another embodiment of the presentinvention, the aqueous phase of the aqueous “suspension S” comprising atleast one earth alkali hydrogen carbonate has a magnesium ionconcentration from 1 to 200 mg/l, preferably from 2 to 150 mg/l, andmost preferably from 3 to 125 mg/l.

According to one embodiment of the present invention, the resultingaqueous solution after the at least one membrane filtration unit has acalcium concentration from 1 to 700 mg/l, preferably from 50 to 650mg/l, and most preferably from 70 to 630 mg/l. According to anotherembodiment of the present invention, the aqueous solution after the atleast one membrane filtration unit comprising at least one earth alkalihydrogen carbonate has a magnesium concentration from 1 to 200 mg/l,preferably from 2 to 150 mg/l, and most preferably from 3 to 125 mg/l.

Additionally or alternatively, the resulting aqueous solution after theat least one membrane filtration unit has a turbidity value of lowerthan 1.0 NTU, preferably of lower than 0.5 NTU, and most preferably oflower than 0.3 NTU.

“Turbidity” in the meaning of the present invention describes thecloudiness or haziness of a fluid caused by individual particles(suspended solids) that are generally invisible to the naked eye. Themeasurement of turbidity is a key test of water quality and can becarried out with a nephelometer. The units of turbidity from acalibrated nephelometer as used in the present invention are specifiedas Nephelometric Turbidity Units (NTU).

In one preferred embodiment of the present invention, the at least onemixing unit comprises a heating device capable of heating the content ofthe at least one mixing unit to a desired temperature. The content ofthe at least one mixing unit is typically adjusted with the heatingdevice to a temperature from 5° C. to 90° C. and preferably from 20° C.to 50° C. For example, the content of the at least one mixing unit isadjusted with the heating device to a temperature from 20° C. to 40° C.and preferably from 20° C. to 30° C.

It is appreciated that the heating device may be any kind of heatingmeans known to the man skilled in the art for controlling and adjustingthe temperature in a vessel and/or tank.

The aqueous suspension S formed in the at least one mixing unit hassolids content in the range from 0.1 to 50 wt.-%, preferably in therange of 3 to 35 wt.-%, more preferably in the range of 5 to 25 wt.-%,based on the total weight of the resulting suspension S. The particlesobtained in the resulting suspension S represent a total particlesurface area (SSA_(total)) that is at least 5 000 m²/tonne of theresulting “suspension S”. The suspension S can be prepared in the mixingunit by mixing water, mineral powder and/or a suspension (also calledslurry) of calcium carbonate.

At least a part of the resulting suspension S obtained in the at leastone mixing unit is filtered by passing at least a part of the resultingsuspension S through at least one membrane filtration unit in order toobtain an aqueous solution comprising at least one earth alkali hydrogencarbonate and, furthermore, at least a part of the particles of theresulting suspension S is subjected to a particle dividing step. It hasto be noted that at least a part of the filtering of the resultingsuspension S takes place parallel to the particle dividing step.

The resulting suspension S may be withdrawn intermittently orcontinuously from the at least one mixing unit through at least oneoutlet located at the at least one mixing unit. Intermittent withdrawalmay be arranged, for instance, by using periodically opening valves,rotating valves, settling legs and the like. Continuous withdrawal istypically arranged by using a continuously operating control valve. Theposition of the one or more valves used for intermittent or continuouswithdrawal is adjusted such that it is underneath the typical fillingheight of the resulting suspension in the at least one mixing unit.Preferably, the one or more valves used for intermittent or continuouswithdrawal is positioned at the bottom of the at least one mixing unit.

One specific requirement of the present inventive is thus that theinstallation comprises at least one dividing unit comprising dividingmeans.

It is appreciated that the at least one dividing unit refers to a devicecapable of dividing solid particles and gas bubbles such that a reducedsize of particles and/or gaseous bubbles in the obtained suspension isobserved.

The at least one dividing unit may be any kind of device well known tothe man skilled in the art and typically used for dividing and orreducing the particle size of solid particles in suspensions comprisingminerals, pigments and/or fillers.

In one preferred embodiment of the present invention, the at least onedividing unit is any kind of grinding device and/or crushing device. Inone preferred embodiment of the present invention, the at least onedividing unit is a grinding device. For example, the at least onedividing unit may be any conventional grinding device in whichrefinement predominantly results from impacts with a secondary body,e.g. a ball mill, a rod mill, a vibrating mill, a centrifugal impactmill, an annular gap bead mill, a vertical bead mill, an attrition mill,or other such equipment known to the skilled person.

In one preferred embodiment of the present invention, the at least onedividing unit is selected from a vertical grinding device and/orvertical crushing device. Alternatively, the at least one dividing unitis a horizontal grinding device and/or horizontal crushing device.

According to yet another embodiment of the present invention, the atleast one dividing unit is at least one dividing device capable toreduce both the size of solid particles and that of gaseous bubbles.This embodiment has the advantage that two process steps, i.e. thereduction of the size of the solid particles and the size of the gaseousbubbles, can be carried out in only one component of the installation,in this case the dividing unit. As a consequence, there is no need fortwo different components to achieve the reduction of the size of thesolid particles and the size of the gaseous bubbles, which results incost and space savings as well as an optimal particle size of bothreactants at the same time.

One dividing unit that may be particularly incorporated in the inventiveinstallation is a conical annular gap bead mill. Preferred is a conicalannular gap bead mill in which the milling zone is created in the gapbetween a conical working vessel—the stator—and a conical rotor. The gapis preferably in the range of 4 mm to 25 mm, more preferably in therange of 5 mm to 20 mm and most preferably in the range of 6 mm to 15mm, in the range of 6.5 mm to 13 mm. The movement of the rotor createsradial movement of the grinding media (metal, glass or ceramic beads).Momentum amplifies the outward motion, so that the product shear forceincreases steadily during the milling operation. Dividing means such asmilling (or grinding) beads are automatically re-introduced into theproduct flow as it enters the milling chamber, so that continuouscirculation of the media in the milling chamber is achieved. Thegeometry of the grinding chamber ensures uniform particle size anddistribution. Product is fed by an external pump with variable flowrate. The peripheral speed of the rotor, the width of the milling gap,the material and diameter of grinding media, media fill volume and flowvelocity can be used to influence the result of particle size reduction.Each of these parameters can be varied at will to create the optimumconditions for each product.

Annular gap bead mills are known to the skilled man. One annular gapbead mill that may be suitable for the inventive installation includesthe annular gap bead mills available from Romaco FrymaKoruma, Germany asFrymaKoruma CoBall MS12, FrymaKoruma CoBall MS18, FrymaKoruma CoBallMS32 or FrymaKoruma CoBall MS50.

It is appreciated that the at least one dividing unit comprises dividingmeans. The dividing means may be selected from any kind of grindingmeans known to the skilled person and typically used for wet grinding.In particular, any kind of grinding means is suitable that is wearresistant under typical conditions used for wet grinding, especiallyunder neutral to alkaline conditions (more precisely at a pH of 6 orabove, preferably at a pH between 6 and 13 and more preferably at a pHbetween 6 and 11) and/or at temperatures above 10° C. (more precisely ata temperature between 10 and 90° C., preferably at a temperature between15 and 70° C. and more preferably at a temperature between 20 and 50°C.).

In one preferred embodiment of the present invention, the dividing meansare moving beads, preferably moving beads of mostly irregular shape. Inthis regard, it is appreciated that the dividing means being part of theat least one dividing unit have a weight median particle diameter d₅₀value of from 0.01 mm to 100 mm, preferably from 0.1 mm to 75 mm andmost preferably from 0.5 mm to 5 mm.

The dividing means, preferably in form of moving beads, being part ofthe at least one dividing unit are made of a mineral, pigment and/orfiller material. In one preferred embodiment of the present invention,the minerals, pigments and/or fillers to be purified and/or prepared arepreferably made of the same material.

For example, if the minerals, pigments and/or fillers to be purified aremarble, the dividing means are also made of marble. If the minerals,pigments and/or fillers to be purified are limestone, the dividing meansare also made of limestone. If the minerals, pigments and/or fillers tobe purified are chalk, the dividing means are also made of chalk. If theminerals, pigments and/or fillers to be purified are dolomite, thedividing means are also made of dolomite. It is thus appreciated thatthe dividing means are preferably made of marble, limestone, chalk,dolomite and mixtures thereof.

Alternatively, the dividing means, preferably in form of moving beads,being part of the at least one dividing unit and the minerals, pigmentsand/or fillers to be purified and/or to be prepared are preferably madeof different materials. In this case, the material of the beads may beselected independently from the material of the minerals, pigmentsand/or fillers to be purified and/or prepared.

Accordingly, it is appreciated that the dividing means, preferably inform of moving beads, being part of the at least one dividing unit aremade of a material selected from the group comprising quartz sand,glass, porcelain, zirconium oxide, zirconium silicate and mixturesthereof, optionally comprising minor quantities of further minerals.

In one preferred embodiment of the present invention, the dividing meansare melt blends of zirconium oxide and cerium oxide and/or yttriumoxide, most preferably the dividing means consist of a mixture of 80 to84 wt.-% zirconium oxide and 20 to 16 wt.-% cerium oxide.

In this regard, at least a part of the suspension S prepared in the atleast one mixing unit is subjected to said at least one dividing unitfor the size reduction of the particles contained in the suspension Sand the gaseous bubbles. In a preferred embodiment the at least onedividing unit is a grinding and/or crushing device, and is mostpreferably a grinding device. The size reduction of the particlescontained in the suspension S and the gaseous bubbles in the at leastone dividing unit provides the benefit that the (chemical) reactionspeed in the inventive installation is increased by continuouslyproducing a freshly prepared and hence active surface of the substancecomprising at least one earth alkali carbonate and the optional at leastone earth alkali hydroxide. In addition, this size reduction of theparticles contained in the suspension S and the gaseous bubbles in theat least one dividing unit enables a continuous operation of theprocess.

In one preferred embodiment of the invention, the aqueous suspensionobtained after the at least one dividing unit has a hardness from 5 to130° dH, preferably from 10 to 60° dH, and most preferably from 15 to50° dH.

For the purpose of the present invention, the hardness refers to theGerman hardness and is expressed in “degree German hardness, ° dH”. Inthis regard, the hardness refers to the total amount of earth alkaliions in the aqueous solution comprising the earth alkali hydrogencarbonate, and is measured by complexometric titration at pH 10 usingethylene-diamine-tetra-actetic acid (EDTA) and Eriochrome T asequivalent point indicator.

The aqueous suspension obtained after the at least one dividing unit haspreferably a pH in the range of 6.5 to 9, preferably in the range of 6.7to 7.9, and most preferably in the range of 6.9 to 7.7, at 20° C.

Additionally or alternatively, the aqueous phase of the aqueoussuspension obtained after the at least one dividing unit has a calciumion concentration from 1 to 700 mg/l, preferably from 50 to 650 mg/l,and most preferably from 70 to 630 mg/l. According to anotherembodiment, the aqueous phase of the aqueous suspension obtained afterthe at least one dividing unit has a magnesium ion concentration from 1to 200 mg/l, preferably from 2 to 150 mg/l, and most preferably from 3to 125 mg/l.

According to still another embodiment of the present invention, theaqueous phase of the aqueous suspension obtained after the at least onedividing unit has a turbidity value of lower than 1.0 NTU, preferably oflower than 0.5 NTU, and most preferably of lower than 0.3 NTU.

The inventive installation comprises the at least one dividing unit suchthat it is assembled in a parallel arrangement with regard to the atleast one membrane filtration unit or introduced in the at least onemixing unit. The at least one dividing unit can be arranged in such away that only a part of the resulting suspension S that is contained inthe at least one mixing unit passes through the at least one dividingunit before circulating back into the at least one mixing unit(“parallel arrangement”). If the at least one dividing unit isintroduced in the at least one mixing unit, a part or all of theresulting suspension S passes the at least one dividing unit.

Before and/or parallel to and/or after the resulting suspension S of theat least one mixing unit passes the at least one dividing unit, thesuspension S passes at least one membrane filtration unit.

One specific requirement of the present inventive is thus that theinstallation comprises at least one membrane filtration unit providedwith at least one inlet and at least one outlet.

It is appreciated that the at least one membrane filtration unit isconnected to the at least one mixing unit. Preferably, the at least onemembrane filtration unit is connected to the at least one mixing unitsuch that the filtrand or retentate obtained in the at least onemembrane filtration unit is circulated back into the at least one mixingunit of the inventive installation.

The term “filtrand or retentate” in the meaning of the presentapplication refers to the part of the suspension S that is retained inthe at least one membrane filtration unit because it cannot pass throughthe pores of the membrane being part of the membrane filtration unit andthus has not passed through the filter system of the at least onemembrane filtration unit.

The at least one membrane filtration unit being part of the installationmay be any kind of membrane filter known to the skilled person andtypically used for filtering aqueous suspensions comprising minerals,pigments and/or fillers. For example, a microfiltration membrane and/oran ultrafiltration membrane may be used.

It is appreciated that there is a pressure difference between the insideof the membrane filtering unit and the surrounding environment so thatsuspended particles are separated from the suspension and a clearsolution is obtained. Preferably, the pressure inside the membranefiltering unit is higher than the pressure of the surroundingenvironment.

A micro filtration membrane is a membrane having a pore size between 0.1and 10 μm and is typically used to separate suspended particles fromsuspension. Microfiltration membranes may be of ceramic, polymer, orother synthetic materials. Preferably, said membranes have backpulsecapability, i.e., a reverse flow of the filtrate by pressure through themembrane to the concentrated side of the aqueous suspension removesbuildup of contaminants which tend to reduce the flow rate of themembrane. In contrast thereto, an ultrafiltration membrane is a membranehaving a pore size between 0.001 and 0.1 μm and is used to separateemulsions, proteins and macromolecules from suspension. The materials ofconstruction are typically the same as for microfiltration membranes.Ultrafiltration membranes are either backpulsed as described above, orbackwashed by closing a filtrate valve for a period of time.

For example, the at least one membrane filtration unit is a cross flowmembrane filtration device. In one preferred embodiment of the presentinvention, the at least one membrane filtration unit is a cross flowmembrane microfiltration device. Additionally or alternatively, the atleast one membrane filtration unit is a cross flow membraneultrafiltration device.

Cross flow membrane filtration devices are known to the skilled man. Onecross flow membrane filtration device that may be suitable for theinventive installation includes the cross flow membrane filtrationdevice available from Microdyn-Nadir GMBH, Germany as Mycrodyn Modul CMB150.

It is appreciated that the at least one membrane filtration unitcomprises at least one platy filter and/or tube filter and/or capillaryfilter membrane. Preferably, the at least one membrane filtration unitcomprises at least one tube filter membrane. If the at least onemembrane filtration unit comprises at least one tube filter membrane,the tube filter membrane preferably has an inner diameter of the tube of0.01 mm to 25 mm, more preferably of 0.1 mm to 10 mm and most preferablyof 0.1 to 7.5 mm. For example, the tube filter membrane has an innerdiameter of the tube of 1 mm to 7.5 mm and preferably of 2.5 mm to 7.5mm.

If the at least one membrane filtration unit comprises at least onecapillary filter membrane, the capillary filter membrane preferably hasan inner diameter of the capillary of 0.01 mm to 0.5 mm, and morepreferably of 0.05 mm to 0.2 mm.

Tube filter membranes are preferred as they provide excellent flowconditions for the separation of solids at relatively low operatingpressures and a high recirculation flow rate, as turbulent flow isproduced at the membrane surface.

In one preferred embodiment of the present invention, the at least onemembrane filtration unit comprises at least one membrane having a poresize of between 0.01 μm and 10 μm, preferably between 0.05 and 5 μm andmost preferably between 0.1 and 2 μm.

It is further appreciated that the speed of flow across the at least onemembrane of the cross flow membrane filtration device is between 0.1 m/sand 10 m/s, preferably between 0.5 m/s and 5 m/s and most preferablybetween 1 m/s and 4 m/s. Additionally or alternatively, the pressure atthe inlet of the cross flow membrane filtration device is between 0 barand 30 bar, preferably between 0.2 bar and 10 bar and most preferablybetween 0.5 and 5 bar.

In one preferred embodiment of the present invention, the at least onemembrane is made of a material selected from the group comprising asintered material, porous porcelain, synthetic polymers, likepolyethylene, polypropylene or Teflon®, and mixtures thereof.

In one preferred embodiment of the invention, the aqueous solutionobtained after the at least one membrane filtration unit has a hardnessfrom 5 to 130° dH, preferably from 10 to 60° dH, and most preferablyfrom 15 to 50° dH.

The aqueous solution obtained after the least one membrane filtrationunit has preferably a pH in the range of 6.5 to 9, preferably in therange of 6.7 to 7.9, and most preferably in the range of 6.9 to 7.7, at20° C.

Additionally or alternatively, the aqueous solution obtained after theleast one membrane filtration unit has a calcium concentration from 1 to700 mg/l, preferably from 50 to 650 mg/l, and most preferably from 70 to630 mg/l. According to another embodiment, the aqueous solution obtainedafter the least one membrane filtration unit has a magnesiumconcentration from 1 to 200 mg/l, preferably from 2 to 150 mg/l, andmost preferably from 3 to 125 mg/l.

According to still another embodiment of the present invention, theaqueous solution obtained after the least one membrane filtration unithas a turbidity value of lower than 1.0 NTU, preferably of lower than0.5 NTU, and most preferably of lower than 0.3 NTU.

The inventive installation comprises the at least one membranefiltration unit such that it is assembled in a parallel arrangement withregard to the at least one dividing unit and/or in serial arrangement ifthe at least one dividing unit is introduced in the at least one mixingunit. The at least one membrane filtration unit may be arranged suchthat only a part of the resulting suspension S that is contained in theat least one mixing unit is fed into the at least one membranefiltration unit before the obtained filtrand or retentate (i.e. the partof the suspension S that is retained in the at least one membranefiltration unit because it cannot pass through the pores of the membranebeing part of the membrane filtration unit) is circulated back into theat least one mixing unit. If the at least one dividing unit isintroduced in the at least one mixing unit, a part or all of theresulting suspension S is fed into the at least one membrane filtrationunit such that the obtained filtrand or retentate is circulated back tothe at least one dividing unit that is introduced in the at least onemixing unit. One specific requirement of the inventive installation isthat the required units being part of the installation are connected influid communication. In other words, the single units of theinstallation are connected directly or indirectly by one or more tubesor pipes provided within, through and/or between the units such that thefluid connecting conduit (or pipeline) is extended out from an outlet ofone unit and connected with an inlet of another unit.

It is thus appreciated that the installation comprises at least threeoutlets, preferably at least four outlets and more preferably at leastfive outlets. In one preferred embodiment of the present invention, theinstallation comprises at least three outlets or at least five outlets.Additionally or alternatively, the installation comprises at least fourinlets, preferably at least five inlets and more preferably at least sixinlets. In one preferred embodiment of the present invention, theinstallation comprises at least five inlets or at least six inlets.

For example, the installation comprises at least three outlets,preferably at least four outlets and more preferably at least fiveoutlets or at least four inlets, preferably at least five inlets andmore preferably at least six inlets. Alternatively, the installationcomprises at least three outlets, preferably at least four outlets andmore preferably at least five outlets and at least four inlets,preferably at least five inlets and more preferably at least six inlets.In particular, the installation comprises at least three outlets and atleast five inlets, e.g. three outlets and five inlets. Alternatively,the installation comprises at least five outlets and at least sixinlets, e.g. five outlets and six inlets.

Preferably, all outlets provided with the installation are liquidoutlets.

One specific requirement of the inventive installation is that the atleast one mixing unit is provided with at least two inlets and at leastone outlet.

In one preferred embodiment of the present invention, the at least onemixing unit is provided with at least two outlets. Additionally oralternatively, the at least one mixing unit is provided with at leastthree inlets, preferably at least four inlets. Preferably, the at leastone mixing unit is provided with at least one outlet and at least threeinlets, preferably at least four inlets. For example, the at least onemixing unit is provided with one outlet and three inlets, preferablyfour inlets. In another preferred embodiment of the present invention,the at least one mixing unit is provided with at least two outlets andat least three inlets, preferably at least four inlets. For example, theat least one mixing unit is provided with two outlets and three inlets,preferably four inlets. In one preferred embodiment of the presentinvention, the at least one mixing unit is provided with multiple inletsand multiple outlets.

It is preferred that at least one inlet located at the at least onemixing unit is a powder inlet.

It is further appreciated that the at least one membrane filtration unitis provided with at least one inlet and at least one outlet. Preferably,the at least one membrane filtration unit is provided with at least oneinlet and at least two outlets. More preferably, the at least onemembrane filtration unit is provided with multiple inlets and multipleoutlets.

One specific requirement is that at least one outlet of the at least onemixing unit is connected to at least one inlet of the at least onemembrane filtration unit and at least one outlet of the at least onemembrane filtration unit is connected to at least one inlet of the atleast one mixing unit. In this regard, it is appreciated that thefiltrand or retentate obtained in the at least one membrane filtrationunit is recirculated back into the at least one mixing unit of theinventive installation.

In one embodiment of the present invention, at least a part of thefiltrate, i.e. the filtered aqueous solution comprising a soluble saltof the minerals, pigments and/or fillers obtained by passing theresulting suspension S through the filter system of the at least onemembrane filtration unit, can be discharged from the at least onemembrane filtration unit. Accordingly, the at least one membranefiltration unit is preferably equipped with an outlet suitable fordischarging of at least a part of the filtered aqueous solutioncomprising a soluble salt of the minerals, pigments and/or fillers.

The purification of minerals, pigments and/or fillers and/or preparationof precipitated earth alkali carbonates and/or mineralization of watermay be carried out in that CO₂ is introduced into the installation. Inone preferred embodiment of the present invention, at least one inletprovided with the installation is a gas inlet. Preferably, the at leastone gas inlet is a CO₂ inlet. For example, the inventive installationcomprises one gas inlet.

It is appreciated that the at least one gas inlet may be located at themixing unit and/or between the at least one mixing unit and the at leastone dividing unit. In one preferred embodiment of the present invention,the at least one gas inlet is located at the mixing unit or between theat least one mixing unit and the at least one dividing unit.

If the at least one gas inlet is located between the at least one mixingunit and the at least one dividing unit, the gas inlet is preferably aventuri injector. More preferably, the venturi injector is locatedbetween the outlet of the at least one mixing unit and the inlet of theat least one dividing unit. In the meaning of the present patentapplication a venturi injector is a pump-like device that uses theVenturi effect of a converging-diverging nozzle to convert the pressureenergy of a motive fluid to velocity energy which creates a low pressurezone that draws in and entrains a fluid by suction. After passingthrough the throat of the injector, the mixed fluid expands and thevelocity is reduced which results in recompressing the mixed fluids byconverting velocity energy back into pressure energy. The motive fluidmay be a liquid, steam or any other gas. The fluid entrained by suctionmay be a gas, a liquid, a slurry, or a dust-laden gas stream.

The venturi injector can be located before (i.e. closer to the mixingunit) or after (i.e. closer to the dividing unit) the at least one pumpthat is located between the at least one mixing unit and the at leastone dividing unit. One advantage of the use of a venturi injector isthat a gas, e.g. CO₂ that is produced by the power generation can beintroduced in the process that can be carried out with the inventiveinstallation, so that the process can be almost run CO₂ neutral.

In one preferred embodiment of the present invention, the at least onegas inlet is located at the at least one mixing unit. For example, theat least one gas inlet may be located such that an introduction of gasinto the aqueous suspension comprising at least one earth alkalicarbonate and optionally at least one earth alkali hydroxide isobtained.

In another preferred embodiment of the present invention the stirringdevice is combined with a gas inlet such that a sufficient mixing oragitation is obtained in the aqueous suspension comprising at least oneearth alkali carbonate and optionally at least one earth alkalihydroxide.

For example, if the at least one dividing unit is integrated in the atleast one mixing unit, at least one inlet being a gas inlet is locatedat the top of the hollow shaft of the stirring device of the at leastone mixing unit.

A flow control valve or other means may be used to control the rate offlow of carbon dioxide into the suspension comprising minerals, pigmentsand/or fillers to be purified. For example, a CO₂ dosing block and a CO₂in-line measuring device may be used to control the rate of the CO₂flow. The carbon dioxide dosage is preferably controlled by the pH ofthe produced aqueous earth alkali hydrogen carbonate solution.

Accordingly, it is appreciated that the at least one mixing unitcomprises at least two inlets being liquid inlets. Preferably, the atleast one mixing unit comprises at least three liquid inlets and morepreferably at least four liquid inlets.

In one preferred embodiment of the present invention, the at least onemixing unit comprises at least two inlets being liquid inlets, morepreferably at least three inlets being liquid inlets and at least oneinlet being a gas inlet. For example, the at least one mixing unitcomprises two inlets being liquid inlets, more preferably three inletsbeing liquid inlets and one inlet being a gas inlet. Preferably, the atleast one mixing unit comprises three inlets being liquid inlets and oneinlet being a gas inlet.

In another preferred embodiment of the present invention, the at leastone mixing unit comprises at least three inlets being liquid inlets,more preferably at least four inlets being liquid inlets.

In case at least one gas inlet is located at the at least one mixingunit, the at least one mixing unit is preferably further provided withat least three inlets being liquid inlets. For example, the at least onemixing unit is provided with one inlet being a gas inlet and threeinlets being liquid inlets.

Additionally or alternatively, the at least one mixing unit furthercomprises at least one inlet being a powder inlet.

According to one embodiment of the present invention, the at least onedividing unit comprises at least one inlet and at least one outlet.Preferably, the at least one dividing unit comprises one inlet and oneoutlet. In one preferred embodiment of the present invention, the atleast one dividing unit is provided with multiple inlets and multipleoutlets.

In one preferred embodiment of the present invention, at least oneoutlet of the at least one mixing unit is connected to at least oneinlet of the at least one dividing unit and at least one outlet of theat least one dividing unit is connected to at least one inlet of the atleast one mixing unit.

Alternatively, the at least one dividing unit is integrated in the atleast one mixing unit. Preferably, if the at least one dividing unit isintegrated in the at least one mixing unit, at least one inlet being agas inlet is located at the top of the hollow shaft of the stirringdevice of the at least one mixing unit.

Preferably, if at least one outlet of the at least one mixing unit isconnected to at least one inlet of the at least one dividing unit and atleast one outlet of the at least one dividing unit is connected to atleast one inlet of the at least one mixing unit, at least one inletbeing a gas inlet is located between the at least one mixing unit andthe at least one dividing unit. More preferably, if at least one outletof the at least one mixing unit is connected to at least one inlet ofthe at least one dividing unit and at least one outlet of the at leastone dividing unit is connected to at least one inlet of the at least onemixing unit, at least one inlet being a gas inlet is located between afeed pump of the at least one dividing unit and the at least onedividing unit. Most preferably, at least one inlet being a gas inlet islocated at the inlet of the at least one dividing unit.

If at least one inlet being a gas inlet is located between the at leastone mixing unit and the at least one dividing unit, the at least onemixing unit is preferably only provided with liquid inlets. Preferably,the at least one mixing unit is provided with at least three liquidinlets, more preferably at least four liquid inlets. For example, the atleast one mixing unit is provided with four liquid inlets.

In one preferred embodiment of the present invention, the installationcomprises at least one control unit regulating the filling level of theat least one mixing unit, pump speed, pH, conductivity, calcium ionconcentration (e.g. by ion sensitive electrode) and/or temperature. Theat least one control unit regulating the filling level of the at leastone mixing unit, pump speed, pH, conductivity, calcium ion concentration(e.g. by ion sensitive electrode) and/or temperature may be operatedcollectively or separately.

The flow of fluid from one unit being part of the installation toanother unit being part of the installation may be achieved by way ofone or more intermediate (and not specifically mentioned or described)devices, pumps or apparatuses. Furthermore, such flow may or may not beselectively interruptible such as by valves, switches, control unitsand/or other suitable components.

In one preferred embodiment of the present invention, the installationcomprises at least one pump, preferable at least two pumps and mostpreferably at least three pumps for directing the aqueous suspension Sfrom one unit of the installation to another unit being part of theinstallation. For example, the installation comprises at least one pumplocated between the at least one mixing unit and the at least onemembrane filtration unit. The pump is preferably designed such that theaqueous suspension S is directed from the at least one mixing unit tothe at least one membrane filtration unit.

Additionally or alternatively, the installation comprises at least onepump located between the at least one mixing unit and the at least onedividing unit. The pump is preferably designed such that the aqueoussuspension S is directed from the at least one mixing unit to the atleast one dividing unit. It is appreciated that the at least one pumplocated between the at least one mixing unit and the at least onemembrane filtration unit is preferably a venturi injector. Morepreferably, the venturi injector is located between the outlet of the atleast one mixing unit and the inlet of the at least one dividing unit.For example, the venturi injector is located at the connection such asthe tubes or pipes between the at least one mixing unit and the at leastone dividing unit. It is noted that the foregoing only applies to theembodiments where the at least one dividing unit is not integrated inthe mixing unit.

In one preferred embodiment of the present invention, the installationcomprises at least two pumps, one located between the at least onemixing unit and the at least one membrane filtration unit and onelocated between the at least one mixing unit and the at least onedividing unit.

For example, if the at least one dividing unit is integrated in the atleast one mixing unit, the installation preferably comprises only onepump located between the at least one mixing unit and the at least onemembrane filtration unit. Otherwise, the installation preferablycomprises two pumps. If the installation comprises two pumps, one pumpis preferably located between the at least one mixing unit and the atleast one membrane filtration unit while the other one is preferablylocated between the at least one mixing unit and the at least onedividing unit.

It is further appreciated that the pumping capacity of the at least onepump (in m³/h of the sum) feeding the at least one membrane filtrationunit is 0.01 to 100 times the volume of the at least one mixing unit.

Additionally or alternatively, the ratio of the pumping capacity of theat least one pump (in m³/h of the sum) feeding the at least one dividingunit to the pumping capacity of the at least one pump (in m³/h of thesum) feeding the at least membrane filtration unit is between 1:1 and1:1000. Preferably, the ratio of the pumping capacity of the at leastone pump (in m³/h of the sum) feeding the at least one dividing unit tothe pumping capacity of the at least one pump (in m³/h of the sum)feeding the at least membrane filtration unit is between 1:5 and 1:250.

In a preferred embodiment of the present invention, the installation isprovided such that a continuous purification of minerals, pigmentsand/or fillers and/or preparation of precipitated earth alkali carbonateis achieved. However, the installation of the present invention can alsobe provided such that a semi-batch mode for the purification ofminerals, pigments and/or fillers and/or preparation of precipitatedearth alkali carbonate is achieved. In this case, the resultingsuspension S can, for example, represent a total particle surface thatis around 1 000 000 m²/tonne and is provided to the installation of thepresent invention. Then, the product, i.e. the aqueous solution of theearth alkali hydrogen carbonate, is discharged from the installationuntil the remaining resulting suspension S represents a total particlesurface that is around 1 000 m²/tonne, and then a new amount of the atleast one substance comprising at least one earth alkali carbonate andthe optional at least one earth alkali hydroxide in a minor amount inrespect to the earth alkali carbonate provided to the installation ofthe present invention. It is noted that the total particle surface canbe determined during each point of the continuous installation bydetermining the specific surface area (SSA_(total)) of the aqueoussuspension S as well as the dry content of the aqueous suspension S.

If the installation is provided in a continuous mode, the installationis preferably controlled by the amount of discharged aqueous solutioncomprising at least one earth alkali hydrogen carbonate. The amount ofdischarged aqueous solution comprising at least one earth alkalihydrogen carbonate may be determined by a volumetric method, e.g. by aflow meter, or by a gravimetric method, e.g. by using a scale. Thisvalue, i.e. the amount of discharged aqueous solution comprising atleast one earth alkali hydrogen carbonate, is preferably used to controlthe (fresh) feed water valve.

The measurement of the solid content of the aqueous suspension S iscarried out gravimetrically.

In one preferred embodiment of the present invention, the various unitsof the installation may be collectively or separately supplied withelectricity for operation.

Preferably, at least a part or all of the electrical power required forthe present installation is derived from solar power, for example fromthermal and/or voltammetry solar panels.

The resulting suspension S that is obtained has preferably solidscontent in the range from 0.1 to 80 wt.-%, preferably in the range from3 to 50 wt.-%, more preferably in the range from 5 to 35 wt.-%, based onthe total weight of the resulting suspension S. Additionally oralternatively, the particles in the suspension S that is obtained afterthe at least one dividing unit represent a specific surface area(SSA_(total)) of from 5 000 to 5 000 000 m²/tonne of the resultingsuspension S, preferably of from 10 000 to 5 000 000 m²/tonne of theresulting suspension S, and more preferably of from 70 000 to 500 000m²/tonne of the resulting suspension S, for example 100 000 to 500 000m²/tonne.

The resulting suspension S and/or aqueous solution that is obtainedafter the at least one dividing unit and/or the at least one membranefiltration unit preferably comprises at least one earth alkali hydrogencarbonate.

According to one embodiment of the present invention, the aqueoussuspension S and/or aqueous solution obtained after the at least onedividing unit and/or the at least one membrane filtration unitpreferably comprises a calcium hydrogen carbonate, preferably in anamount of 25 to 150 mg/l and/or a magnesium hydrogen carbonate,preferably in an amount of >0 to 50 mg/l. Additionally or alternatively,the aqueous suspension S and/or aqueous solution obtained after the atleast one dividing unit and/or the at least one membrane filtration unitpreferably comprises a mixture of a calcium and a magnesium hydrogencarbonate, preferably in a total amount of 25-200 mg/l.

In one preferred embodiment of the present invention, the aqueoussuspension S and/or aqueous solution obtained after the at least onedividing unit and/or the at least one membrane filtration unitpreferably comprises 45 mg/l calcium hydrogen carbonate, or 80 to 120mg/l calcium hydrogen carbonate and 20 to 30 mg/l magnesium hydrogencarbonate.

A mixture of calcium and a magnesium hydrogen carbonate can be obtainedwhen dolomite, half burned and/or fully burned dolomite containingmaterial is used as the substance comprising the earth alkali carbonate.In the meaning of the present invention burned dolomite comprisescalcium oxide (CaO) and magnesium oxide (MgO), whereas half burntdolomite comprises Mg in the form of magnesium oxide (MgO) and Ca in theform of calcium carbonate (CaCO₃), but can also include some minoramount of calcium oxide (CaO).

By heating the resulting permeate solution that is obtained after the atleast one dividing unit and the at least one membrane filtration unit,water is evaporated from the solution and upon a certain point of timethe earth alkali carbonate starts to precipitate out of the solution.

Said heating of the resulting permeate solution that is obtained afterthe at least one dividing unit and the at least one membrane filtrationunit may be achieved in the at least one mixing unit comprising aheating device. Alternatively, the resulting permeate solution obtainedafter the at least one dividing unit and the at least one membranefiltration unit may be directed to another mixing unit comprising aheating device.

In one preferred embodiment of the present invention, the permeatesolution is typically adjusted with the heating device to a temperaturefrom 45° C. to 90° C. and preferably from 55° C. to 80° C.

The invention is explained in the following in more detail in connectionwith the drawings with reference to two embodiments of installations.

As shown in FIG. 2, one embodiment of the inventive installationcomprises a mixing unit (1) equipped with a stirrer (2), at least oneinlet for water (14) and the minerals, pigments and/or fillers (6) to bepurified and/or prepared, either in a dry or in an aqueous form.Connected with an outlet of the mixing unit (1), there is a membranefiltration unit (4) provided with at least one inlet and at least oneoutlet, where at least a part of the resulting suspension S obtained inthe mixing unit (1) is fed to. The membrane filtration unit (4)preferably retains coarse particles that are contained in the aqueoussuspension S, i.e. all particles having a size of at least 0.2 μm. Atleast a part of the resulting suspension S that exits the membranefiltration unit (4) is recirculated back through a connection (12) suchas tubes or pipes into the mixing unit (1). Accordingly, the membranefiltration unit (4) is connected to the mixing unit such that thecontent of the membrane filtration unit (4) can be recirculated to themixing unit (1). In particular, it is to be noted that the filtrand orretentate obtained in the membrane filtration unit (4) is recirculatedback into the mixing unit (1). One specific requirement of the inventiveinstallation thus is that the at least one outlet of the mixing unit (1)is connected to at least one inlet of the membrane filtration (4) unitand at least one outlet of the membrane filtration unit (4) is connectedto at least one inlet of the mixing unit (1).

Optionally, at least a part of the filtered aqueous solution comprisinga soluble salt of the minerals, pigments and/or fillers to be purifiedand/or prepared, i.e. the filtrate (10), may be discharged through anoutlet from the membrane filtration unit (4). Accordingly, the membranefiltration unit (4) may be equipped with another outlet for dischargingof at least a part of the aqueous solution comprising a soluble salt ofthe minerals, pigments and/or fillers, i.e. the filtrate (10) obtainedby passing the resulting suspension S through the filter system of theat least one membrane filtration unit (4).

The discharged solution comprising a soluble salt of the minerals,pigments and/or fillers, i.e. the filtrate (10), may, optionally, besubjected to further treatments (16) such as for example a mechanicaltreatment, preferably by a degasing device, such as for example by anultrasonic and/or vacuum device. Most preferably the resulting gas phaseobtained by the degasing device is re-injected via a gas pipe into theprocess by a venturi injector, such as tubes or pipes, between themixing unit (1) and dividing unit (18) and the vacuum is preferablyproduced by this venturi injector. In addition biocides or otheradditives can be added to the process in order to change the pH of thesolution (e.g. addition of a base such as NaOH), the conductivity of thesolution, or the hardness of the solution. As a further option, theclear aqueous solution comprising a soluble salt of the minerals,pigments and/or fillers, i.e. the filtrate (10), discharged from themembrane filtration unit (4) can be diluted with further water. Thecoarse mineral, pigment and/or filler particles contained in the aqueoussuspension S and that are retained in the filtering device canoptionally be recirculated to the reactor, i.e. into the at least onemixing unit (1), in order to be available for further conversion and/orpurification.

In parallel to the membrane filtration unit (4), the installationcomprises a dividing unit (18) comprising dividing means. The grindingdevice (18) is connected to the mixing unit (1) in such a way that atleast a part of the content of the dividing unit (18) can berecirculated to the mixing unit (1). Accordingly, at least one outlet ofthe mixing unit (1) is connected to at least one inlet of the dividingunit (18). Furthermore, at least one outlet of the dividing unit (18) isconnected to at least one inlet of the mixing unit (1).

A part of the resulting suspension S obtained in the mixing unit (1)having a pH of between 6 and 9 is fed through a connection (8), such astubes or pipes, to the membrane filtration unit (4), whereas anotherpart of the resulting suspension S obtained in the mixing unit (1)having a pH of between 6 and 9 is fed to the dividing unit (18). In thisembodiment, the CO₂ (22) is preferably fed into the installation beforethe dividing unit (18). The resulting ground aqueous suspension obtainedafter the dividing unit (18) is then circulated (24) from the dividingunit (18) back to the mixing unit (1).

As shown in FIG. 3, one embodiment of the inventive installationcomprises a mixing unit in which a dividing unit (1) is integrated. Thecombined mixing/dividing unit (1) is equipped with a stirrer (2) andadditional dividing means such as grinding beads. Furthermore, theinstallation comprises at least one inlet for water (14) and theminerals, pigments and/or fillers (6) to be purified and/or prepared,either in a dry or in an aqueous form. Connected with an outlet of thecombined mixing/dividing unit (1), there is a membrane filtration unit(4) provided with at least one inlet and at least one outlet, where atleast a part of the resulting suspension S obtained in the combinedmixing/dividing unit (1) is passed through. The membrane filtration unit(4) preferably retains coarse particles that are contained in theaqueous suspension, i.e. all particles having a size of at least 0.2 μm.At least a part of the resulting suspension S that exits the membranefiltration unit (4) is recirculated back through a connection (12), suchas tubes or pipes, into the combined mixing/dividing unit (1).Accordingly, the membrane filtration unit (4) is connected to thecombined mixing/dividing unit (1) such that the content of the membranefiltration unit (4) can be recirculated to the combined mixing/dividingunit (1). In particular, it is to be noted that the filtrand orretentate obtained in the membrane filtration unit (4) is circulatedback into the combined mixing/dividing unit (1). One specificrequirement of the inventive installation thus is that the at least oneoutlet of the combined mixing/dividing unit (1) is connected to at leastone inlet of the membrane filtration (4) unit and at least one outlet ofthe membrane filtration unit (4) is connected to at least one inlet ofthe combined mixing/dividing unit (1).

Optionally, at least a part of the filtered aqueous solution comprisinga soluble salt of the minerals, pigments and/or fillers to be purifiedand/or prepared, i.e. the filtrate (10), may be discharged through anoutlet from the membrane filtration unit (4). Accordingly, the membranefiltration unit (4) may be equipped with another outlet for dischargingof at least a part of the aqueous solution comprising a soluble salt ofthe minerals, pigments and/or fillers, i.e. the filtrate (10) obtainedby passing the resulting suspension S through the filter system of theat least one membrane filtration unit (4).

The discharged solution comprising a soluble salt of the minerals,pigments and/or fillers, i.e. the filtrate (10) may, optionally, besubjected to further treatments (16) such as for example a mechanicaltreatment or the addition of biocides or other additives in order tochange the pH of the solution (e.g. addition of a base such as NaOH),the conductivity of the solution, or the hardness of the solution. As afurther option, the clear aqueous solution comprising a soluble salt ofthe minerals, pigments and/or fillers discharged from the membranefiltration unit (4) can be diluted with further water. The coarsemineral, pigment and/or filler particles contained in the suspension andthat are retained in the filtering device can optionally be recirculatedto the reactor, i.e. into the combined mixing/dividing unit (1), inorder to be available for further conversion and/or purification.

Accordingly, at least a part of the resulting suspension S obtained inthe combined mixing/dividing unit (1) having a pH of between 6 and 9 isfed through a connection (8), such as tubes or pipes, to the membranefiltration unit (4). In this embodiment, the CO₂ (22) is preferably fedinto the combined mixing/dividing unit (1) of the installation.Preferably, the stirrer (2) is a mixing machine, wherein a simultaneousmixing of the aqueous suspension and dosing of CO₂ (4) is possible.

FIG. 4 shows a venturi injector (26) that can be used as gas inlet withthe installation according to the present invention. The venturiinjector is a pump-like device that uses the Venturi effect of aconverging-diverging nozzle to convert the pressure energy of a motivefluid to velocity energy which creates a low pressure zone that draws inand entrains a fluid by suction. After passing through the throat of theinjector, the mixed fluid expands and the velocity is reduced whichresults in recompressing the mixed fluids by converting velocity energyback into pressure energy. The motive fluid may be a liquid, steam orany other gas. The fluid entrained by suction may be a gas, a liquid, aslurry, or a dust-laden gas stream.

In the present case, the venturi injector is used to suck CO₂ gas in thesuspension S that is coming from the mixing unit in order to obtain theaqueous suspension S that contains bubbles of CO₂.

The venturi injector can be located before (i.e. closer to the mixingunit) or after (i.e. closer to the dividing unit) the at least one pumpthat is located between the at least one mixing unit and the at leastone dividing unit. One advantage of the use of a venturi injector isthat a gas, e.g. CO₂ that is produced by the power generation can beintroduced in the process that can be carried out with the inventiveinstallation, so that the process can be almost run CO₂ neutral.

FIGURES

FIG. 1 illustrates an installation as described in the prior art.

FIG. 2 illustrates an embodiment of the present installation comprisinga mixing unit, a dividing unit and a membrane filtration unit, whereinat least one outlet of the at least one mixing unit is connected to atleast one inlet of the at least one membrane filtration unit and atleast one outlet of the at least one membrane filtration unit isconnected to at least one inlet of the at least one mixing unit.

FIG. 3 illustrates an embodiment of the present installation comprisinga dividing unit integrated in the mixing unit and a membrane filtrationunit, wherein at least one outlet of the at least one mixing unit isconnected to at least one inlet of the at least one membrane filtrationunit and at least one outlet of the at least one membrane filtrationunit is connected to at least one inlet of the at least one mixing unit.

FIG. 4 illustrates a venturi injector that can be used as gas inlet withthe installation according to the present invention.

The scope and interest of the invention will be better understood basedon the following examples which are intended to illustrate certainembodiments of the invention and are non-limitative.

EXAMPLES Specific Surface Area (SSA) of a Material

The specific surface area (SSA) was measured using a Malvern Mastersizer2000 (based on the Fraunhofer equation).

Particle Size Distribution (Mass % Particles with a Diameter<X) andWeight Median Diameter (d₅₀) of a Particulate Material

Weight median grain diameter and grain diameter mass distribution of aparticulate material were determined using a Malvern Mastersizer 2000(based on the Fraunhofer equation).

pH of an Aqueous Suspension or Solution

The pH was measured using a Mettler-Toledo pH meter. The calibration ofthe pH electrode was performed using standards of pH values 4.01, 7.00and 9.21.

Solids Content of an Aqueous Suspension

The suspension solids content (also known as “dry weight”) wasdetermined using a Moisture Analyser HR73 from the companyMettler-Toledo, Switzerland, with the following settings: temperature of120° C., automatic switch off 3, standard drying, 5 to 20 g ofsuspension.

Turbidity

The turbidity was measured with a Hach Lange 2100AN IS LaboratoryTurbidimeter and the calibration was performed using StabCal turbiditystandards (formazine standards) of <0.1, 20, 200, 1000, 4000 and 7500NTU.

Determination of the Hardness (German Hardness; Expressed in “° dH”)

The hardness refers to the total amount of earth alkali ions in theaqueous suspension comprising the earth alkali hydrogen carbonate, andit is measured by complexometric titration usingethylene-diamine-tetra-actetic acid (EDTA; trade name Titriplex III) andEriochrome T as equivalent point indicator.

EDTA (chelating agent) forms with the ions Ca²⁺ and Mg²⁺ soluble, stablechelate complexes. 2 ml of a 25% ammonia suspension, an ammonia/ammoniumacetate buffer (pH 10) and Eriochrome black T indicator were added to100 ml of a water sample to be tested. The indicator and the buffer isusually available as so-called “indicator-buffer tablet”. The indicator,when masked with a yellow dye, forms a red colored complex with the Ca²⁺and Mg²⁺ ions. At the end of the titration, that is when all ions arebound by the chelating agent, the remaining Eriochrome black T indicatoris in its free form which shows a green color. When the indicator is notmasked, then the color changes from magenta to blue. The total hardnesscan be calculated from the amount of EDTA that has been used.

Table 1 below shows a conversion for the different units of the waterhardness.

TABLE 1 Conversion for the different units of the water hardness^([1]) °dH ° e ° fH ppm mval/l mmol/l German Hardness 1° dH = 1 1.253 1.78 17.80.357 0.1783 English Hardness 1° e = 0.798 1 1.43 14.3 0.285 0.142French Hardness 1° fH = 0.560 0.702 1 10 0.2 0.1 ppm CaCO₃ (USA) 1 ppm =0.056 0.07 0.1 1 0.02 0.01 mval/l Earth alkali ions 1 mval/l = 2.8 3.515 50 1 0.50 mmol/l Earth alkali ions 1 mmol/l = 5.6 7.02 10.00 100.02.00 1 ^([1])In this regard the unit ppm is used in the meaning of 1mg/l CaCO₃.

Comparative Installation

A general process flow sheet of the installation used for thecomparative example is shown in FIG. 1 (Device A). The installationcomprises a feed tank having a feed tank volume of 50 l, which was fedwith 45 l of suspension, as mixing unit including a stirrer and acrossflow membrane microfilter, wherein the suspension comprisingminerals, pigments and/or fillers introduced into the mixing unit iswithdrawn through an outlet locate at the mixing unit and directed andpassed through the crossflow membrane microfilter. At least a part ofthe filtrate exiting the crossflow membrane micro filter is directedback to the mixing unit. The cross flow membrane microfilter has a totalmembrane area of 0.6 m² (3 modules serial of 0.2 m²/module) and an innertube diameter of 6 mm.

Inventive Installations

A general process flow sheet of one installation according to thepresent invention is shown in FIG. 2 (Device B). The installationcomprises a feed tank having a feed tank volume of 50 l, which was fedwith 45 l of suspension, as mixing unit including a stirrer and acrossflow membrane microfilter and a dividing unit which are installedin parallel. The suspension comprising minerals, pigments and/or fillersintroduced into the mixing unit may thus be withdrawn simultaneously orindependently through at least two outlets located at the mixing unitand directed and passed through the crossflow membrane micro filterand/or dividing unit. At least a part of the filtrate exiting thecrossflow membrane micro filter and/or the suspension exiting thedividing unit is directed back to the mixing unit. The cross flowmembrane microfilter has a total membrane area of 0.6 m² (3 modulesserial of 0.2 m²/module) and an inner tube diameter of 6 mm.

A general process flow sheet of another installation according to thepresent invention is shown in FIG. 3 (Device C). The installationcomprises a mixing unit in which the dividing unit is integrated andequipped with a stirrer and grinding beads made of zirconium oxide. Theinstallation further comprises a crossflow membrane microfilter suchthat the suspension comprising minerals, pigments and/or fillersintroduced into the mixing/dividing unit is withdrawn through an outletlocated at the mixing/dividing unit and directed and passed through thecrossflow membrane microfilter. At least a part of the filtrate exitingthe crossflow membrane microfilter is directed back to themixing/dividing unit.

The feed water used in the inventive examples was obtained from an ionexchange equipment of Christ, Aesch, Switzerland Type Elite 1BTH, thefeed water having the following water specification after the ionexchanger:

Sodium 169 mg/l  Calcium   2 mg/l Magnesium <1 mg/l °dH 0.3

Example 1 Microdol A Extra (Dolomite)

In the present example, Microdol A extra a dolomite obtained from theCompany Norwegian Talc, Knarrevik, was used as the at least one earthalkali carbonate.

The goal of the trials in Example 1 was to produce a suspension of earthalkali hydrogen carbonate of a pH of 7.2±0.1 out of dolomite at ambienttemperature. The dolomite feed material at the beginning of the trialhad a d₁₀ of 0.35 μm, a d₅₀ of 2.75 μm and a d₉₀ of 10.53 μm.

The reaction and operation conditions are given in Tables 2 and 3

Comparative: Trial a) Device A, (Tank Temperature 23° C.)

Feed flow to the cross flow membrane microfilter: 2.0 m³/h

TABLE 2 Feed solids l/h of Membrane l/h/m² d₁₀ wt.-%/running CO₂ ° dHl/h of Permeate pressure Permeate pH d₅₀ time in minutes ml/min PermeatePermeate at 10° dH [bar] at 10° dH permeate d₉₀ 15 wt.-% 200 32.5 43 1382 231 7.14 0.35 μm 180 min 2.68 μm 10.5 μm

Inventive: Trial b) Device B, (Tank Temperature 25° C.)

Feed flow to the cross flow membrane microfilter: 2.0 m³/h

Feed flow to the dividing device: 0.20 m³/h

TABLE 3 Feed solids l/h of Membrane l/h/m² d₁₀ wt.-%/trial CO₂ ° dH l/hPermeate pressure Permeate pH d₅₀ running time ml/min Permeate Permeateat 10° dH [bar] at 10° dH permeate d₉₀ 15 wt.-% 250 50 40 209 2 349 7.30.28 μm 165 min. 1.05 μm 3.74 μm

From Table 3 (invention) it can be gathered that the capacity ofpermeate in l/h/m² using the inventive equipment is increased by afactor of 1.5 compared to the capacity of permeate obtained in a priorart equipment as outlined in Table 2 (prior art). In particular, themedium particle diameter (d₅₀) of particles in the suspension S obtainedin the inventive equipment was determined as being 1.05 μm, while themedium diameter (d₅₀) of particles in the suspension S using the priorart equipment stays nearly constant. Turbidity of the permeate sampleobtained in the inventive equipment and taken after 165 min. was <0.3NTU.

Example 2 Microdol A Extra (Dolomite)

In the present example, Microdol A extra a dolomite as described inExample 1 was used as the at least one earth alkali carbonate.

The goal of the trials in Example 2 was to produce a suspension of earthalkali hydrogen carbonate of a pH of 7.8±0.1 out of dolomite at anincreased temperature of 40° C.

The Dolomite feed material at the beginning of the trial had a d₁₀ of0.35 μm, a d₅₀ of 2.75 μm and a d₉₀ of 10.53 μm.

The reaction and operation conditions are given in Table 4.

Inventive: Trial c) Device B, (Tank Temperature 40° C.)

Feed flow to the cross flow membrane microfilter: 2.0 m³/h

Feed flow to the dividing device: 0.20 m³/h

TABLE 4 Feed solids l/h of Membrane l/h/m² d₁₀ wt.-%/trial CO₂ ° dH l/hPermeate pressure Permeate pH d₅₀ running time ml/min Permeate Permeateat 10° dH [bar] at 10° dH permeate d₉₀ 8 wt.-% 100 38 74 280 1 467 7.70.32 μm 165 min 1.26 μm 3.72 μm

From Table 4 it can be gathered that the capacity of permeate in l/h/m²using the inventive equipment at 40° C. is increased by a factor of 1.33compared to the capacity of permeate obtained in the inventive equipmentat 25° C. and compared to the prior art equipment as outlined in Table 2(prior art) even by a factor of 2.0. The Examples clearly show theimprovement of efficiency of the inventive installations of Trial b) andc) versus Trial a).

Example 3 Raw Marble, Carinthia, Austria

In the present example, a raw marble from the region of Carinthia,Austria was used. The HCl insoluble content was 7.5 wt.-% (approx. 90 wt% mica and 10 wt.-% quartz, determined by XRD).

The Marble feed material at the beginning of the trial had a d₁₀ of 1.0μm, a d₅₀ of 24.5 μm and a d₉₀ of 104 μm. The specific surface area(SSA) was <0.1 m²/g.

The reaction and operation conditions of the installation can begathered from Table 5.

Trial d), Device B, (Mix Tank Temperature 24° C.)

Feed flow to the cross flow membrane microfilter: 2.0 m³/h

Feed flow to the dividing device: 0.065 m³/h

TABLE 5 d₁₀ Feed solids l/h of Membrane l/h/m² d₅₀ wt.-%/trial CO₂ ° dHl/h Permeate pressure Permeate pH d₉₀ running time ml/min PermeatePermeate at 10° dH [bar] at 10° dH permeate SSA 5 wt.-% 200 25 5.4 13.50 23 7.17 0.30 μm 105 min 1.18 μm 6.16 μm 3.07 m²/g 5 wt.-% 300 42.542.2 179 1 299 6.7 0.32 μm 165 min 1.2 μm 5.56 μm not determined 5 wt.-%300 40.0 79.6 318 2 351 6.7 not 180 min determined

The total particle surface area (SSA_(total)) of the suspension Sobtained in the inventive equipment and taken after 105 min. represented185000 m²/tonne of suspension S.

Turbidity of the permeate sample obtained in the inventive equipmenttaken after 165 min. was <0.3 NTU.

2 liters of clear permeate obtained after 180 min were heated for 2 h at70° C., and the resulting precipitate was collected by filtering using alaboratory membrane filter disc having a diameter of 50 mm and a poresize of 0.2 μm (produced by Millipore).

The XRD analysis of the resulting precipitate shows the following:

Aragonitic PCC 97.3 wt.-% Calcitic PCC   2.7 wt.-% Silica/Silicates(Mica) <0.1 wt.-% HCl insol. <0.1 wt.-%

Hence, the XRD results and the HCl insoluble content show that a veryclean CaHCO₃ solution as well as very pure precipitated calciumcarbonate is obtained from a starting material that contains a HClinsoluble content (impurities) of 7.5 wt.-%.

This example clearly demonstrates that the inventive installationproduces very pure extraction solutions as well as minerals, pigmentsand/or fillers out of impure starting material. This example shows theuse of the inventive installation as a cost efficient alternative toprocesses where chemicals are used to separate the mineral, pigmentand/or filler phases.

Example 4 Dolomite/Limestone Blend Pilot Plant Trial

In the present example, one part Microdol A extra a dolomite asdescribed in Example 1 was mixed with two parts of limestone of theregion of Avignon, France, and was used as the blend of earth alkalicarbonates.

The goal of the trial in Example 4 was to produce a solution of earthalkali hydrogen carbonate of a pH of 6.5 to 6.7 in pilot scale.

The blend of earth alkali carbonates had a d₁₀ of 0.43 μm, a d₅₀ of 2.43μm and a d₉₀ of 6.63 μm at the beginning of the trial.

The blend was fed as 50 wt.-% suspension in water.

The reaction and operation conditions of the installation can begathered from Table 6.

Inventive: Trial e) Device B, (Tank Temperature 18.5° C.)

The installation comprises a feed tank having a feed tank volume of1,000 l as mixing unit including a stirrer and a crossflow polyethylenemembrane micro filter as the crossflow membrane microfiltration unit anda dividing unit which are installed in parallel. The suspensioncomprising minerals, pigments and/or fillers introduced into the mixingunit may thus be withdrawn simultaneously or independently through atleast two outlets located at the mixing unit and directed and passedthrough the crossflow membrane micro filtration unit and/or dividingunit. At least a part of the filtrate exiting the crossflow membranemicrofiltration unit and/or the suspension exiting the dividing unit isdirected back to the mixing unit. The cross flow polyethylene membranemicrofilter has a total membrane area of 8 m², an inner tube diameter of5.5 mm and is 3 m long. Furthermore, the micro filter has a porediameter of 1.0 μm and comprises 174 tubes in parallel (Seprodyn filtermodule SE 150 TP 1L/DF, Microdyn).

Feed water: deionized water obtained from an ion exchange equipment ofChrist, Aesch, Switzerland, (<1 mg/l earth alkali carbonate).

Feed flow of suspension S to the cross flow membrane unit: 36 m³/h,speed across the membranes: 3 m/s.

Pressure at the cross flow membrane inlet: 1 bar

Pressure at the cross flow membrane outlet: 0.3 bar

Pressure at the solution outlet: 0.05 bar

Feed flow of suspension S to the dividing device: 0.40 m³/h

Pressure at the dividing unit inlet: 0.7 to 0.8 bar

Dose of CO₂: 2.0 liter/min at a pressure of 1.5 to 1.6 bar.

Feed solids of suspension S: 15 wt.-%

Results are measured after 44 hours continuous running

TABLE 6 d₁₀ Earth alkali ion m³/h of l/h/m² d₅₀ ° dH m³/h concentrationin Permeate Permeate pH d₉₀ Permeate Permeate the permeate at 10° dH at10° dH permeate SSA 33 0.5 Ca²⁺: 214 mg/l 1.65 0.21 6.7 0.34 μm Mg²⁺: 20mg/l 1.47 μm 4.11 μm 2.72 m²/g

The specific particle surface of the suspension S obtained in theinventive installation and taken after 44 hours was 408,000 m²/tonne ofsuspension S.

A first quality of tap water comprising 45 mg/l earth alkali carbonate(sum of CaCO₃/MgCO₃) was produced by diluting the permeate of this trialwith feed water. The resulting capacity of this trial corresponds toapproximately 6.7 m³/h at a concentration of 45 mg/l earth alkalicarbonate.

A second quality of tap water comprising 100 mg/l earth alkali carbonate1 (CaCO₃) and 10-15 mg/l of earth alkali carbonate 2 (MgCO₃) wasproduced by diluting the permeate of this trial with feed water. Theresulting capacity of this trial corresponds to approximately 2.7 m³/hat a concentration of 100 mg/l CaCO₃ and 10-15 mg/l MgCO₃.

The total electrical power consumption of the inventive installation toobtain 1 m³ of the second quality of tap water was 0.07 to 0.12 kWh perm³ of tap water quality 2.

The electrical power consumption for the mill part of the inventiveinstallation to obtain 1 m³ of the second quality of tap water was0.06-0.09 kWh per m³ of tap water quality 2.

1. Installation for the purification of minerals, pigments and/orfillers and/or the preparation of precipitated earth alkali carbonateand/or mineralization of water, the installation comprising in fluidcommunication a) at least one mixing unit provided with at least twoinlets and at least one outlet, b) at least one dividing unit comprisingdividing means, and c) at least one membrane filtration unit providedwith at least one inlet and at least one outlet, wherein at least oneoutlet of the at least one mixing unit is connected to at least oneinlet of the at least one membrane filtration unit and at least oneoutlet of the at least one membrane filtration unit is connected to atleast one inlet of the at least one mixing unit.
 2. Installationaccording to claim 1, wherein the at least one mixing unit comprises astirring device.
 3. Installation according to claim 1, wherein the atleast one mixing unit comprises a heating device capable of heating thecontent of the at least one mixing unit to a temperature of between 5°C. and 90° C., and preferably between 20° C. and 50° C.
 4. Installationaccording to claim 1, wherein the at least one dividing unit is at leastone grinding device and/or at least one crushing device, and preferablyis at least one grinding device.
 5. Installation according to claim 1,wherein the at least one dividing unit is at least one vertical grindingdevice and/or at least one vertical crushing device or at least onehorizontal grinding device and/or at least one horizontal crushingdevice.
 6. Installation according to claim 1, wherein the at least onedividing unit is a conical annular gap bead mill.
 7. Installationaccording to claim 1, wherein the at least one dividing unit comprisesdividing means having a weight median particle diameter d₅₀ value offrom 0.01 mm to 100 mm, preferably from 0.1 mm to 75 mm and mostpreferably from 0.5 mm to 5 mm.
 8. Installation according to claim 1,wherein the at least one dividing unit comprises moving beads asdividing means made of a material selected from the group comprisingquartz sand, glass, porcelain, zirconium oxide, zirconium silicate andmixtures thereof, optionally comprising minor quantities of furtherminerals.
 9. Installation according to claim 1, wherein the dividingmeans of the at least one dividing unit are made of a mineral, pigmentand/or filler material, preferably the dividing means and the minerals,pigments and/or fillers to be purified and/or to be prepared are of thesame material.
 10. Installation according to claim 1, wherein the atleast one membrane filtration unit is a cross flow membrane filtrationdevice, and preferably is a cross flow membrane microfiltration deviceand/or a cross flow membrane ultrafiltration device.
 11. Installationaccording to claim 10, wherein the cross flow membrane filtration devicecomprises at least one tube filter membrane having an inner diameter ofthe tube from 0.01 mm to 25 mm, preferably from 0.1 mm to 10 mm. 12.Installation according to claim 1, wherein the at least one membranefiltration unit comprises at least one membrane having a pore size ofbetween 0.01 μm and 10 μm, preferably between 0.05 μm and 5 μm and mostpreferably between 0.1 μm and 2 μm.
 13. Installation according to claim12, wherein the membrane material is selected from the group comprisinga sintered material, porous porcelain, synthetic polymers, likepolyethylene, polypropylene or Teflon®, and mixtures thereof. 14.Installation according to claim 10, wherein the speed of flow across theat least one membrane of the cross flow membrane filtration device isbetween 0.1 m/s and 10 m/s, preferably between 0.5 m/s and 5 m/s andmost preferably between 1 m/s and 4 m/s and/or the pressure at the inletof the cross flow membrane filtration device is between 0 bar and 30bar, preferably between 0.2 bar and 10 bar and most preferably between0.5 and 5 bar.
 15. Installation according to claim 1, wherein theinstallation comprises at least three outlets, preferably at least fouroutlets and more preferably at least five outlets and/or theinstallation comprises at least four inlets, preferably at least fiveinlets and more preferably at least six inlets
 16. Installationaccording to claim 1, wherein the at least one mixing unit comprises atleast two outlets and/or at least three inlets, preferably at least fourinlets.
 17. Installation according to claim 1, wherein the installationcomprises at least one gas inlet, preferably a CO₂ inlet. 18.Installation according to claim 1, wherein the at least one mixing unitcomprises at least two inlets being liquid inlets, preferably at leastthree liquid inlets, and more preferably at least four liquid inlets.19. Installation according to claim 1, wherein the installationcomprises at least one control unit regulating the filling level of theat least one mixing unit, pump speed, pH, conductivity, calcium ionconcentration (e.g. by ion sensitive electrode) and/or temperature. 20.Installation according to claim 1, wherein the installation comprises atleast one pump located between the at least one mixing unit and the atleast one membrane filtration unit.
 21. Installation according to claim1, wherein at least one outlet of the at least one mixing unit isconnected to at least one inlet of the at least one dividing unit and atleast one outlet of the at least one dividing unit is connected to atleast one inlet of the at least one mixing unit.
 22. Installationaccording to claim 1, wherein the installation further comprises atleast one pump located between the at least one mixing unit and the atleast one dividing unit.
 23. Installation according to claim 20, whereinthe pumping capacity of the at least one pump (in m³/h of the sum)feeding the at least one membrane filtration unit is 0.01 to 100 timesthe volume of the at least one mixing unit and/or the ratio of thepumping capacity of the at least one pump (in m³/h of the sum) feedingthe at least one dividing unit to the pumping capacity of the at leastone pump (in m³/h of the sum) feeding the at least membrane filtrationunit is between 1:1 and 1:1000 and preferably between 1:5 and 1:250. 24.Installation according to claim 1, wherein the at least one dividingunit is integrated in the at least one mixing unit.
 25. Installationaccording to claim 1, wherein at least one inlet being a gas inlet islocated between the at least one mixing unit and the at least onedividing unit, more preferably between a feed pump of the at least onedividing unit and the at least one dividing unit, and most preferably atthe inlet of the dividing unit.
 26. Installation according to claim 1,wherein the at least one inlet being a gas inlet is a venturi injectorthat is located between the at least one mixing unit and the at leastone dividing unit, and preferably is located between the outlet of theat least one mixing unit and the inlet of the at least one dividingunit.
 27. Installation according to claim 24, wherein at least one inletbeing a gas inlet is located at the top of the hollow shaft of thestirring device of the at least one mixing unit.
 28. A process for thepurification of minerals, pigments and/or fillers and/or themineralization of water comprising processing minerals using the aninstallation according to claim
 1. 29. A process for the preparation ofprecipitated earth alkali carbonate using installation according toclaim 1.